1. Field of the Invention
The present invention relates to the field of treatment or prevention of hemorrhagic viral infections.
2. Description of the Background Art
Hemorrhagic fever viruses (HFVs) are viruses classified in several taxonomic families. HFVs cause a variety of disease syndromes with similar clinical characteristics, referred to as acute hemorrhagic fever syndromes. The pathophysiologic hallmarks of HFV infection are microvascular damage and increased vascular permeability. HFVs that are RNA viruses include Arenaviridae such as Lassa, as well as South American hemorrhagic fevers including Junin, Machupo, Guanarito, and Sabia viruses, which are the causative agents of Lassa fever and Argentine, Bolivian, Venezuelan, and Brazilian hemorrhagic fevers, respectively, whitewater Arroyo virus and Flexal virus; Filoviridae (Ebola and Marburg viruses); Bunyaviridae: Crimean-Congo hemorrhagic fever virus (CCHFV), Rift Valley fever virus, hemorrhagic fever with renal syndrome-associated hantaviruses, including Hantaan virus, Seoul virus, Dobrava virus (also referred to as Dobrava-Belgrade virus), and Puumala virus, and hantavirus pulmonary syndrome-associated hantaviruses, including Bayou virus, Black Creek Canal virus, New York virus, Sin Nombre virus, Andes virus, Oran virus, Juquitiba virus, Laguna Negra virus, and Lechiguanas virus; and Flaviviridae (dengue, dengue fever, dengue hemorrhagic fever, dengue shock syndrome, Kyasanur Forest disease, Omsk hemorrhagic fever, yellow fever).
Under natural conditions, humans are infected through the bite of an infected arthropod or through contact with infected animal reservoirs. Hemorrhagic fever viruses are highly infectious by aerosol; are associated with high morbidity and, in some cases, high mortality; and are thought to pose a serious risk as biologic weapons.
The exact pathogenesis for HFVs varies according to the etiologic agent. The major target organ is the vascular endothelium. Immunologic and inflammatory mediators are thought to play an important role in the pathogenesis of HFVs. All HFVs can produce thrombocytopenia, and some also cause platelet dysfunction. Infection with Ebola and Marburg viruses, Rift Valley fever virus, and yellow fever virus causes destruction of infected cells. Disseminated intravascular coagulation (DIC) is characteristic of infection with Filoviridae. Ebola and Marburg viruses may cause a hemorrhagic diathesis and tissue necrosis through direct damage to vascular endothelial cells and platelets with impairment of the microcirculation, as well as cytopathic effects on parenchymal cells, with release of immunologic and inflammatory mediators. Arenaviridae, on the other hand, appear to mediate hemorrhage via the stimulation of inflammatory mediators by macro-phages, thrombocytopenia, and the inhibition of platelet aggregation.
The incubation period of HFVs ranges from 2 to 21 days. The clinical presentations of these diseases are nonspecific and variable, making diagnosis difficult. It is noteworthy that not all patients will develop hemorrhagic manifestations. Even a significant proportion of patients with Ebola virus infections may not demonstrate clinical signs of hemorrhage.
Initial symptoms of the acute HFV syndrome may include fever, headache, myalgia, rash, nausea, vomiting, diarrhea, abdominal pain, arthralgias, myalgias, and malaise. Illness caused by Ebola, Marburg, Rift Valley fever virus, yellow fever virus, Omsk hemorrhagic fever virus, and Kyasanur Forest disease virus are characterized by an abrupt onset, whereas Lassa fever and the diseases caused by the Machupo, Junin, Guarinito, and Sabia viruses have a more insidious onset. Initial signs may include fever, tachypnea, relative bradycardia, hypotension (which may progress to circulatory shock), conjunctival injection, pharyngitis, and lymphadenopathy. Encephalitis may occur, with delirium, seizures, cerebellar signs, and coma. Most HFVs cause cutaneous flushing or a macular skin rash, although the rash may be difficult to appreciate in dark-skinned persons and varies according to the causative virus. Hemorrhagic symptoms, when they occur, develop later in the course of illness and include petechiae, purpura, bleeding into mucous membranes and conjunctiva, hematuria, hematemesis, and melena. Hepatic involvement is common, and renal involvement is proportional to cardiovascular compromise.
Laboratory abnormalities include leukopenia (except in some cases of Lassa fever), anemia or hemoconcentration, and elevated liver enzymes; DIC with associated coagulation abnormalities and thrombocytopenia are common. Mortality ranges from less than 1% for Rift Valley fever to 70% to 90% for Ebola and Marburg virus infections
The nonspecific and variable clinical presentation of the HFVs presents a considerable diagnostic challenge. Clinical diagnostic criteria based on WHO surveillance standards for acute hemorrhagic fever syndrome include temperature greater than 101 F (38.3 C) of less than 3 weeks' duration; severe illness and no predisposing factors for hemorrhagic manifestations; and at least two of the following hemorrhagic symptoms: hemorrhagic or purple rash, epistaxis, hematemesis, hematuria, hemoptysis, blood in stools, or other hemorrhagic symptom with no established alternative diagnosis. Laboratory techniques for the diagnosis of HFVs include antigen detection, IgM antibody detection, isolation in cell culture, visualization by electron microscopy, immunohistochemical techniques, and reverse transcriptase-polymerase chain reaction.
Current therapy for HFVs is largely supportive, but ribavirin has been used with some benefit, depending on the agent. HFV patients tend to respond poorly to fluid infusions and rapidly develop pulmonary edema.
There remains a need in the art for methods of treatment or prevention of hemorrhagic viral infections.